Page 137 - Blog Posts v1

Using these data, I calculated the threshold (minimum) fluences that would be required to induce a reaction in those ink colours with those wavelengths (see above). Note that these fluences will be for the most superficial ink particles – higher fluences will be necessary for deeper ink.
The above curves show that black responds well to all the wavelengths at a low fluence (around 2 J/cm2).
Blue and green respond at a lower fluence with the ruby and alex wavelengths compared with the Nd:YAG wavelengths - as observed in real life.
However, when we look at the red and yellow colours, the minimum fluences required for the ruby, alex and Nd:YAG fundamental (1064nm) jump up significantly. Only the YAG doubled line, 532nm, stays relatively low.
This all agrees with clinical experience – the 532nm wavelength is the natural choice for the ‘sunset’ colours (red, orange, yellow), while ruby and alex lasers are usually suggested for blues and greens.
However, it is not that simple!! I made a video showing how we can be ‘deceived’ by what we see. While we may not be able to discriminate between various ink colours in the skin, the laser wavelengths will react to the different colours according to their absorption profiles.
Never trust your eyes!!
Mike’s Blog Posts 137